1. Field of the Invention
The present invention relates to a line switching method and an asynchronous transfer mode (ATM) exchange using the method.
2. Description of the Related Art
FIG. 6 shows an outline of an asynchronous transfer mode (ATM) exchange. In FIG. 6, subscribers SUB are accommodated respectively in subscriber circuits 1 of the ATM exchange. Additionally, a prescribed number of subscriber circuits 1 are connected to a line concentration and distribution device 2.
The line concentration and distribution device 2 attaches to a cell of call information, a path information tag of an output path and a subscriber circuit, to which the cell is output, and is sent to the switch section 3.
The switch section 3 switches the cell according to the attached path information and connects it to the line concentration and distribution device 2, again. Then, the line concentration and distribution device 2 determines a subscriber circuit 1, to which the called subscriber is connected, according to the path information (tag). After removing the path information of the cell, the cell is connected to the determined subscriber circuit 1.
In other words, a format of the cell input to the line concentration and distribution device 2 is as shown in FIGS. 7A and 7B. As shown in FIGS. 7A, a virtual path identifier (VPI) and a virtual channel identifier (VCI) are included in a header section, and further, the information corresponding to the VPI and VPI is provided in a payload section.
The VPI and VCI distinguish user information and signal information, and send the cell as it is, if it is the signal information, according to the VPI and VCI to a signal processor, not shown in FIGS. 7A and 7B. On the other hand, if it is the user information, switching information A for path setting in a switching section 3 and distribution information B for identifying a subscriber circuit are attached in the cell as a tag to send to the switching section 3.
When a call is generated in this mode, a call processor 4 of the ATM exchange analyzes the cell of the outgoing call. As a result, tags are attached, as shown in FIG. 7B, to specify both of the input and output subscriber circuit 1 and the line concentration and distribution device 2.
In the conventional method, if the same line concentration and distribution device 2 is used for the incoming call and the outgoing call, the switch section 3 sets a path according to the switching information A of the tag for line switching.
In other words, in FIG. 6, when a call from a subscriber accommodated in a subscriber circuit 1 linked to a line concentration and distribution device 2 is addressed to a subscriber connected to a subscriber circuit 1 connected to the same line concentration and distribution device 2, i.e., the destination is the same line concentration and distribution device, the call is passed through the switch section 3 in the exchange, thus making a resource of the switch section be consumed.
Accordingly, it is an object of the present invention to realize an operational environment where a resource usage of a switching section 3 can be reduced and operations for connection can be facilitated in high speed even if a failure occurs in the switching section 3.
The above-described object is achieved by a line switching method in an asynchronous transfer mode exchange according to the present invention, which includes a line concentration and distribution device, to which a subscriber circuit for accommodating a plurality of subscribers is connected and a switching section, the line switching method comprising the steps of comparing information for identifying a path of a subscriber""s cell with information registered in a monitor table, detecting that a first subscriber circuits for accommodating a called subscriber is connected to a same line concentration and distribution device to which a second subscriber circuit for accommodating a calling subscriber is connected, and looping back and connecting the call sent from the calling subscriber to the called subscriber without passing through the switching section.
To carrying out the present invention in one preferred mode, the information registered in the monitor table is controlled by a call processor.
Further, the above-described object is achieved by an asynchronous transfer mode exchange according to the present invention including a line concentration and distribution device, to which a subscriber circuit for accommodating a plurality of subscribers is connected, and a switching section, comprising, a loop back circuit corresponding to the line concentration and distribution device, wherein the loop back circuit loops back and connects a call sent from a calling subscriber to a called subscriber without passing through the switching section when the loop back circuit detects both of subscriber circuits for storing the calling subscriber and called subscriber are connected to a same line concentration and distribution device.
Alternatively, in another mode, the line concentration and distribution device further comprises a monitor table for maintaining subscribers"" information stored in the subscriber circuit connected to the line concentration and distribution device and the loop back circuit compares the subscribers"" information registered in the monitor table with the information for identifying a path of the subscribers"" cell.
Further, in the other mode, the subscribers"" information maintained in the monitor table is registered under a control of a call processor.
Furthermore, the loop back circuit including a monitor table is provided on the preceding or latter part of the line concentration device, the information for identifying a path of the subscribers"" cell is registered in the monitor table, the information for identifying a path of the calling subscribers"" cell is compared with the information for identifying a path of the subscribers"" cell registered in the monitor table, and the call sent from the calling subscriber is looped back and connected to the called subscriber without passing through the switching section when the result of the comparison is a coincidence.
Alternatively, in the other mode, an asynchronous transfer mode exchange according to the present invention includes a line concentration and distribution device, to which a subscriber circuit for accommodating a plurality of subscribers is connected, and a switching section, wherein the line concentration and distribution device includes a line concentrator and a distributor, and there are further comprised of a detecting means for detecting both of subscriber circuits for accommodating a calling subscriber and a called subscriber are connected to a same line concentration according to information for identifying a path of a subscribers"" cell and a tag attaching circuit for identifying a path of a subscribers"" cell provided in the preceding part of the line concentrator, and a multiplexer for multiplexing a cell sent from the switching section with an output from the tag attaching circuit provided in the preceding part of the distributor.
Other objects of the present invention become clear by the description for explaining embodiments according to the attached drawings.
FIG. 1 is a block diagram of a first embodiment according to the present invention.
FIG. 2 is a structural diagram of the first embodiment of the present invention, which includes a loop back circuit 21.
FIG. 3 is a series of operational flowing chart of the first embodiment of FIG. 2.
FIG. 4 shows a block diagram of an other embodiment, in which a loop-back 21 is provided in the latter part of a line concentration and distribution device 2, comparing with the embodiment of FIG. 2.
FIG. 5 shows an embodiment, in which a loop back function is provided in the inside of the line concentration and distribution device 2.
FIG. 6 shows an outline of an asynchronous transfer mode (ATM) exchange.
FIGS. 7A and 7B are explanatory diagrams of a format of a cell input to a line concentration and distribution device.